Strain Ductility Research Articles

Enhanced mechanical properties of lightweight refractory high-entropy alloys at elevated temperatures via Si addition

A new lightweight refractory high-entropy alloys were prepared by introducing Si element into AlMo0.5NbTiV alloy. The effects of Si content on microstructural evolution, density and high temperature mechanical properties were analyzed. The results show that the addition of Si leads to the formation of hard and brittle M5Si3-type (M = Ti and Nb) phase at the grain boundary of the matrix, which gradually transforms the alloys from a single body centered cubic (BCC) structure to a dual-phase structure. While the density of AlMo0.5NbTiVSix alloys decreases from 6.01 to 5.59 g/cm3 with the increase of Si content, and the mechanical properties are also significantly improved, AlMo0.5NbTiVSi0.5 alloy has the best yield strength of 1428 and 390 MPa at 1073 K and 1273 K, respectively. Among them, AlMo0.5NbTiVSi0.1 alloy has the best compression ductility strain at 1073 K, up to 22.2 %, indicating that the addition of appropriate Si can improve the compression ductility of the alloy, which is also caused by the combination of grain refinement and the appearance of eutectic structure. On the one hand, the segregation of Si elements at grain boundaries results in slow growth of the primary crystal, which inhibits the growth of grains. On the other hand, the eutectic structure composed of M5Si3 and BCC is distributed at the grain boundary, which is not conducive to the growth of grains, and the combined effect of the two eventually leads to the grain refinement. The strengthening mechanisms of the alloys can be attributed to the second phase strengthening, solid solution strengthening and grain refinement strengthening. In addition, the softening of the alloys at 1273 K is caused by dynamic recovery and dynamic recrystallization, and the dynamic recovery is the main softening mechanism.

Properties and stress-strain curve of rubberized concrete cast with uncoated or pre-coated rubber with cement/waste materials

Replacement of fine aggregate with crumb rubber (CR) in concrete manufacturing has become necessary to reduce environmental problems resulting from the traditional disposal of waste tires and to produce environment-friendly concrete. The main problem resulting from incorporating CR into the concrete industry remains the reduction in the properties of concrete. Various methods have been employed to treat CR particles to enhance the overall performance of crumb rubber concrete (CRC). Nevertheless, most of the suggested treatment techniques exhibited little efficacy in improving the characteristics of CR particles, and certain chemical treatments pose risks and hazards to the environment. This work presents a novel method for pre-treating CR particles before their use in CRC. The methodology involves the utilization of several processing materials, including cement (C), supplemental cementitious materials (SCM) such as fly ash (FA), and waste materials such as marble powder (MP). Seventeen different mixtures in terms of rubber replacement ratios and rubber processing methods were prepared for the experiment. One mix served as the control without any addition of CR. Four mixtures were generated by substituting varying proportions (5%, 10%, 15%, and 20%) of sand with untreated CR, measured by weight. The remaining twelve mixes contain treated CR with C, FA, and MP. This study investigated the fresh and mechanical properties of CRC, as well as the overall behavior of the stress-strain curve, including yield, peak, ultimate strain, toughness, modulus of elasticity, and strain ductility. The findings indicated that pretreatment of CR with one of the proposed materials enhances the overall behavior of CRC, especially using FA, compared to untreated. The substitution of fine aggregate with 20% CR treated with FA significantly improved the overall properties of CRC. The compressive strength, splitting tensile strength, peak stress, modulus of elasticity, and toughness rose by 22%, 21.30%, 31.19%, 5.30%, and 37%, respectively, compared to using the same proportion of untreated rubber. Therefore, this type of treatment can be relied upon to improve the properties of CRC and give acceptable results.

Mechanical, electrical and self-healing properties of carbon fibre-reinforced ultra-lightweight ECC

The hybrid mixes of carbon fibres (CF), fly ash cenosphere and polyethylene fibre could be used to develop smart ultra-lightweight engineered cementitious composites (ULW-ECCs). In this study, the effects of CF length (1, 3, 6, 9, 12, 15, 20 mm) with different volume fractions (0.0, 0.5 and 1.0 vol%) on the fundamental mechanical (compression, tension and flexure) and electrical properties of CF-reinforced ULW-ECCs were evaluated. Pseudo-strain-hardening indices, multiple micro-cracking behaviours and self-healing properties were also tested. The experimental results reveal that, except for the 1 mm particle CF, incorporating CF could improve the strength (compression, tension and flexure) of ULW-ECCs but decrease the strain ductility properties under tension; and CF lengths of 9- and 12-mm show better results. The electrical conductivity of ULW-ECCs was improved by CF, and the higher dosage further increased the conductivity. The conductivity increased first and then decreased with the increase in CF length and the 9 mm CF (1.0 vol%) shows higher conductivity. The conductive network was affected by the volume fraction, length, count under the same content, and possible fracture of CF. Long CFs work well at low content in forming conductive networks, while short CFs are more effective at high content. The conductivity decreased with the increase of curing age and reached a constant value after 90 d. Incorporating CF and increasing its length/content negatively impacted crack number and width. CF-reinforced ULW-ECCs exhibit excellent self-healing, with reduced ability as wet-dry cycles and curing age increase.

Unified Compressive Strength and Strain Ductility Models for Fully and Partially FRP-Confined Circular, Square, and Rectangular Concrete Columns

Unified Compressive Strength and Strain Ductility Models for Fully and Partially FRP-Confined Circular, Square, and Rectangular Concrete Columns

Effects of steel shim geometric characteristics and imperfections on the behavior of unbonded elastomeric bridge bearings subjected to large lateral displacements

Unbonded laminated elastomeric bridge bearings are designed to accommodate service-level deformations, but during an earthquake they can experience deformation demands that are significantly larger than those for which they were designed. Because these bearings are critical elements of a bridge, they must perform reliably even under seismic-level demands. The effects of the characteristics and condition of the steel shims on the seismic behavior of these bearings have received limited attention in the literature. Yet, the manufacturing process of these bearings sometimes introduces imperfections. For instance, during vulcanization, the steel shims might get rotated or bent. In this context, this paper investigates how manufacturing imperfections and the thickness characteristics of steel shims affect the behavior of unbonded elastomeric bridge bearings subjected to successive cycles of large lateral displacement. Finite element analysis is used to study the deformation pattern of these bearings, their hysteretic response characteristics, and the damageability of their steel shims. It is observed that imperfections can increase a bearing’s roll-off and risk of instability. Imperfections can also increase a bearing’s effective lateral stiffness and damage, quantified though a specific plastic-energy-based damage factor. Plastic damage in the shims is found to be appreciably dependent on their thickness. Under cyclic displacement, damage manifests itself more in the form of spreading of the yielded area rather than increased peak strain ductility. Plastic strains in the steel shims do not get close to the fracture limit, and all the bearings exhibit fairly stable hysteretic loops under the adopted loading protocol.

Multi-objective optimization of high performance concrete columns under compressive loading with potential applications for sustainable earthquake-resilient structures and infrastructures

High performance column composites are multifunctional composites designed to improve resilience of structures and infrastructures to natural and unforeseen multiple loads during service. As a result of their superior mechanical performance, high performance column composites have been found attractive to improve resilience of medium and high-rise buildings as well as long-span structures and infrastructures in earthquake-prone regions. Scientometric analysis revealed limitations of traditional design standards and inadequate earthquake engineering to reduce collosal damage during seismic impact and the need for investment in alternative green energy to reduce anthropogenic-induced earthquakes linked to oil and gas projects. High performance CFRP (carbon fibre reinforced polymer) composite was investigated as potential laminate reinforcement and confinement for recycled concrete column using performance-based Taguchi-Response surface methodology optimization. Though columns wrapped with two layers CFRP confinement and reinforced with internal laminate CFRP reinforcement obtained higher maximum load and favourable failure mode, the optimized result, which comprises column confined with two layers of external CFRP confinement only, obtained 36.3% and 36.19% greater fracture toughness and fracture energy respectively, 1.4 times better displacement ductility index, 2.78 times strain ductility index and comparable load capacity. The superior mechanical performance of high performance recycled concrete column composite and favourable failure mode was attributed to strain hardening effect which depends on the CFRP confinement. Further studies are required to improve the mechanical performance and failure mode of high performance column composite for construction of resilient structures and infrastructures in the built environment.

Bidirectional effect of earthquake on low-rise RC frames with and without the consideration of In-plane effect of unreinforced masonry infill

Low rise RC frames make up the majority of residential structures built in Nepal. They are created in accordance with the requirements outlined in the Nepal Building Code, particularly the mandatory rule of thumb. Only the bare frame model is taken into consideration while analyzing and designing the majority of reinforced concrete structures in Nepal's urban and semi-urban areas. The infill walls' additional impact is often completely disregarded. Furthermore, there are no separate guidelines and standards set by Nepal Building codes for considering the impact of infill masonry during the analysis. Hence, in this study, reinforced concrete frame structures that commonly represent Nepalese low-rise RC frames is subjected to bidirectional (XY) shaking. Four types of models are considered and for each model, two cases are taken: those with and those without taking into account the in-plane effect of unreinforced masonry infill. The infills’ in-plane impact is modeled using a macro modeling approach. The response parameters under investigation are column rebar strain ductility and roof displacement. The results of the analysis clearly indicate that, when the infills’ in-plane effect is taken into account, both the roof displacement and the strain ductility demand of the column are greatly reduced as compared to the situation where it is not. Furthermore, it is obvious from the analytical fragility curves produced for the bare frame and infill models that the structure's vulnerability is exaggerated when the in-plane impact of infill is ignored.

Estimation of deformation capacity of steel beam-columns based on strain ductility coefficient

Estimation of the deformation capacity of steel beam-columns is of high significance in seismic design, especially in the performance-based design of steel structures. Strain-based estimation of the deformation capacity is convenient as it is not susceptible to load and boundary conditions and directly characterises the effect of axial load on the reduction of member ductility. However, owing to the complexity of the strain distribution following local buckling, which is a common phenomenon in steel beam-columns in the ultimate state, it is difficult to determine the strain representative of the deformation of a member. Based on experimental studies of H-section steel beam-columns under cyclic loading, this study investigates the development process of local buckling and plastic deformation and proposes the concept of “equivalent strain” to characterise the deformation in local buckling area. Subsequently, the deformation capacity of steel beam-columns is estimated using the strain ductility coefficient. Finally, by performing regression analysis on the parametric study, an empirical formula is derived in terms of the strain ductility coefficient and verified using the experimental results. The results of this paper can be expected to provide a reference for the performance evaluation of steel beam-column members.

Enhancement of compressive strength and strain ductility of SMA fiber reinforced concrete considering fiber’s aspect ratios

In this study, the effect of recovery stress on the toughness of cementitious materials was investigated using randomly distributed SMA fibers in concrete. The composite was reinforced by cold drawn crimped SMA fibers due to their great potential in developing a prestressing effect as well as providing sufficient bond resistance. To this end, considering the same volumetric fraction, different aspect ratios of the SMA fibers were embedded into the matrix and then molded into different reinforced concrete cylinders. Compression tests were performed where several parameters, including compressive strength, ductility, axial, and volumetric strain were examined before and after inducing the prestressing effect. Furthermore, the present study dealt with fracture modes, as well as internal and surface crack analysis via X-ray and digital image correlation (DIC) equipment to investigate the effect of prestressing with different aspect ratios. The results showed that not only the current geometry of SMA fibers in concrete could improve the ductility of the composite, but also elevate the compressive strength demonstrating a considerable rise in energy absorption capacity.

Enhancing strength and ductility via crystalline-amorphous nanoarchitectures in TiZr-based alloys.

Crystalline-amorphous composite have the potential to achieve high strength and high ductility through manipulation of their microstructures. Here, we fabricate a TiZr-based alloy with micrometer-size equiaxed grains that are made up of three-dimensional bicontinuous crystalline-amorphous nanoarchitectures (3D-BCANs). In situ tension and compression tests reveal that the BCANs exhibit enhanced ductility and strain hardening capability compared to both amorphous and crystalline phases, which impart ultra-high yield strength (~1.80 GPa), ultimate tensile strength (~2.3 GPa), and large uniform ductility (~7.0%) into the TiZr-based alloy. Experiments combined with finite element simulations reveal the synergetic deformation mechanisms; i.e., the amorphous phase imposes extra strain hardening to crystalline domains while crystalline domains prevent the premature shear localization in the amorphous phases. These mechanisms endow our material with an effective strength–ductility–strain hardening combination.

Effect of Oxygen Diffusion During the Post-Processing of Ti6Al4V Lattice Structures Fabricated by the Selective Laser Melting Process

Abstract Post-processing of Ti6Al4V lattice structures fabricated using selective laser melting (SLM) was performed using hot isostatic pressing (HIPing) and heat treatment (HT) to mitigate the undesired effect of rapid cooling during SLM. Oxygen diffusion during post-processing had a significant influence on the microstructure and subsequently the mechanical properties of the lattices. Oxygen content analysis was conducted to confirm the oxygen diffusion through the strurts’ peripheries. The effect of oxygen diffusion during the HIPing and sub-transus HT (600–800 °C) regimes on the phase transformation, failure mechanisms, and mechanical properties of the lattices was investigated. Results revealed that the transformation of the originally formed α′ martensite was dependent on the post-processing temperature. This transformation resulted in a decrease in yield strength. The decrease in failure strain (ductility) for all treated conditions was related to oxygen diffusion, forming near-surface α-case.

Mechanical behavior of high-strength concrete incorporating seashell powder at elevated temperatures

Cement-based composites may experience higher temperatures during their service period due to fire. After fire exposure, the concrete properties may be significantly affected in terms of safety and serviceability. Therefore, to improve the fire resistance of high-strength concrete, it was proposed to add seashells in cementitious composites for improved fire resistance. In this study, the seashell powder was used for concrete (0, 10, 20, and 30%) and plastering mortar (20%, 40%, and 60%) as a replacement of fine aggregate to develop high-strength concrete (HSC). Different properties, such as compressive strength, stress-strain response, elastic modulus, compressive toughness, strain ductility, mass loss of modified and controlled samples, and the deterioration caused by elevated temperatures exposure, were determined. The analyzed formulations were heated to a temperature of 200 °C, 400 °C, 600 °C, and 800 °C at a heating rate of 5 °C/min and then tested for residual conditions. Seashell modified samples showed a higher compressive strength, elastic modulus, and compressive toughness than the control sample at elevated temperature with less spalling sensitivity. According to visual inspection, SS-HSC, compared to HSC, showed less cracking at higher temperatures. Moreover, plastering high-strength concrete with seashell showed greater strength with more fire resistance to the concrete core. Conclusively, the utilization of seashells in high-strength concrete is efficient for fire-resistant concrete.

Complete Stress-Strain Relations of Early-Aged Cementitious Grout under Compression: Experimental Study and Constitutive Model.

The compressive stress–strain behaviors of early-aged cementitious grout specimens were experimentally investigated, and the differences of characteristic parameters of the stress–strain curve and the energy evolution law of each specimen under uniaxial compression were discussed in this study. The results indicate that with an increase in the specimen age, the peak stress, peak strain, ultimate strain, elastic modulus, peak secant modulus, strain ductility coefficient, and energy-dissipation coefficient of the prism specimens gradually improved. Additionally, a comparison of the test results of cementitious grout specimens and concrete specimens with the same age reveals that the peak stress, peak strain, and ultimate strain of cementitious grout specimens were greater than that of concrete specimens, the elastic modulus and peak secant modulus of the specimens were less than that of concrete specimens, and the strain ductility coefficient and energy-dissipation coefficient show no consistent conclusions with respect to the material type. Moreover, comparing the energy evolution curves of specimens with different specimen ages shows that the decrease rate of the elastic strain rate and the increase rate of the dissipated energy rate gradually decreased with the increase in specimen age. The elastic strain rate and dissipated energy rate of the CGM−270 specimen and control specimens were greater than that of other specimens, and the decrease rate of the elastic strain rate was less than that of other specimens. Based on the statistical damage theory, a statistically stochastic damage constitutive model was derived by considering the characteristics of cementitious grout according to the compression test results. A comparison of the proposed models with the experimental results indicated that the proposed stress–strain constitutive models were sufficiently accurate.

Effect of Strain Rate Sensitivity on Fracture of Laminated Rings under Dynamic Compressive Loading

The effects of cladding layers of rate-sensitive materials on the ductility and fracture strain of compressed rings are numerically investigated by using the finite element method (FEM) and employing the Johnson–Cook (J–C) model. The results show that ductility is governed by the behavior of the material that is located at the ring outer wall regardless of the volume fraction of the core and clad materials. However, as the number of layers increases, this influence becomes less noticeable. Moreover, as barreling increases at the outer wall and decreases at the inner wall, fracture strain increases. Furthermore, the effects of ring shape factor and bonding type of clad and core materials are numerically evaluated. The numerical results show that less force per unit volume is required to fracture narrower rings and that using a noise diffusion pattern at the interface of the materials is more suitable to simulate crack propagation in the compressed rings and functionally graded materials (FGMs). Additionally, delamination has a direct relation to layer thickness and can occur even in the presence of perfect bonding conditions owing to differences among the material and fracture parameters of laminated layers.

Partially fly ash and nano-silica incorporated recycled coarse aggregate based concrete: Constitutive model and enhancement mechanism

The single use of nano-silica (NS) or fly ash (FA) can improve the strength of recycled aggregate concrete (RAC). However, the studies on NS-FA-modified RAC (NFRAC) are limited, and further research is required to understand the mechanical behaviors of NFRAC over different curing ages. In this study, to further improve the properties of RAC, these two supplementary cementitious materials (SCMs) were utilized in RAC together: NFRAC. The workability as well as the compressive and split tensile properties were determined by an orthogonal test along with the effects of various factors, including curing age, recycled coarse aggregate (RCA) replacement rate, and SCM content on the performance of NFRAC. NFRAC was found to have adequate mechanical properties, both in the early and later curing ages. Based on NFRAC with 100% RCA replacement rate as the main research object, the strain ductility, energy consumption, and constitutive model were further explored. Scanning electron microscopy was performed to explore the modified mechanism owing to the incorporation of NS and FA. Both the SCMs can successfully accelerate the pozzolanic reaction, thereby improving the mechanical properties. In addition, NS can also fill the micropores in RCAs and react with the CH of mortar to form C–S–H gels, thereby improving the properties of ITZ. However, NS weakens the workability that can be compensated by incorporating spherical FA. Finally, 10% FA and 2% or 3% NS are recommended as SCMs for RAC.

Heat Treatment Effects on Pristine and Cold-Worked Thin-Walled Inconel 625

Thin-walled Inconel 625 sheet metal was sectioned into tensile specimens, plastically strained, and then heat treated. Specimens were pulled to a targeted strain, unloaded, and then subjected to one of two heat treatments with the goal of restoring the full ductility and total plastic strain capability of the material. Post-heat treatment tensile testing was performed at room temperature to evaluate the heat treatment efficacy and then followed by hardness and microstructural analysis. The results showed the amount of material recovery was affected by the initial amount of plastic strain imparted to the tensile specimen before heat treatment. Although recrystallization was not observed, grains did elongate in the load direction, and the Kernel average misorientation (KAM) increased with heat treatment. Furthermore, specimens prestrained to 40% and heat treated at 980 °C successfully recovered 88% of pre-heat treatment strain capability prior to fracturing.

Monotonic and cyclic stress-strain models for confined concrete-masonry shear wall boundary elements

Simulation of the seismic response of fully grouted reinforced masonry shear walls (RMSWs) built with reinforced masonry boundary elements (RMBEs) necessitates reliable nonlinear models of their RMBEs. The axial monotonic and cyclic full stress-strain curves of RMBEs are essential for predicting the lateral cyclic response of RMSWs with boundary elements. Therefore, a reliable stress-strain constitutive model for the axial monotonic and cyclic behavior of RMBEs is required. The authors recently investigated the axial monotonic compressive behavior of unconfined and confined RMBEs built with different section configurations, vertical reinforcement arrangements, transverse confinement ratios, and different construction procedures. In the current study, the authors investigated the cyclic behavior of some RMBEs whose counterparts were previously tested under axial monotonic compression. In addition, more specimens with different confinement configurations and different grout strengths were tested. Comparisons of the test results showed that increasing the vertical reinforcement ratio increased the axial load carrying capacity of the tested RMBEs but decreased their strain ductility. In addition, using a low compressive strength grout significantly reduced the strain ductility of the RMBEs. Moreover, monotonic and cyclic stress-strain models for confined and unconfined concrete-masonry boundary elements subjected to axial compression loading were developed. The proposed models showed good-to-excellent agreement with the experimental results, predicting the stress-strain rising curve, stress drop, and postpeak behavior. Furthermore, unloading and reloading curves, strength degradations, and softening of reversal and reloading branches due to cyclic degradations were well captured by the proposed model.

PERFORMANCE OF SQUARE REINFORCED CONCRETE COLUMNS CONFINED WITH INNOVATIVE CONFINING SYSTEM UNDER AXIAL COMPRESSION

Several structural failures occur in the columndue to the lack of confinement. The circular column is not popular for regular buildings. The use of circular spiral is only familiar tothe circular column. Many design engineers usesquare columns with hoops and cross tiesas confinement. As far as the authors’ knowledge, therewasonly a study carried out on square columnswith circular spirals as confinement. For this reason, the authors propose and introduce a new type of innovative confinement system for square columns using square spiralsas confinement and a combination thereof, which has never been carried out in the previous studies. No code’s provision is also applicable tothis type of confinement.This research was conducted to investigate the performance of each of these new confinement systems as a promising option in the future instead of the traditional confinement. To achieve the objective of the research, a two-phase study was conducted. The first phasewas to analyze the potential, design, formation, and assemblyof the new confinement systemconsisting of a combination of square and circular spirals (SPIL), a combination of octagonal and square spirals (SS8I), an interlocking among square spirals (SPIP), and a plain concrete specimen (PC) as a benchmark. The second phasewas an experimental program that involvesa mix-designof the concrete, preparation of the column specimens with various confinement systems, and the compression tests of the column specimens using a 3500-kN UTM. The test results indicate that the SPIP specimen has higher initial stiffness, peak stress, and strain ductility compared with others.

Experimental investigation of axial compressive behavior of square and rectangular confined concrete-masonry structural wall boundary elements

Reinforced masonry boundary elements (RMBEs) are critical components in determining the lateral response of reinforced masonry structural walls with boundary elements. Fundamental interpretation of the effect of various influential parameters on the RMBEs′ behavior is essential to enhance their stress–strain response. This study investigates, experimentally, the influence of various design parameters and construction procedures on the axial compressive behavior of fully grouted RMBEs built with C-shaped concrete-masonry blocks. Thirty-eight unreinforced and RMBEs were constructed and tested under concentric axial loading till failure. The effect of five parameters, namely, the vertical reinforcement ratio, the volumetric ratio of confinement reinforcement, cross-section configuration, stack pattern and running-bond, and pre-wetting of dry masonry shell before grouting, was investigated. The test results showed that increasing the vertical reinforcement ratio of the RMBEs resulted in a significant increase in the peak compressive stress and a considerable reduction in the corresponding strain ductility. Moreover, as the RMBEs volumetric ratio of transverse reinforcement doubled, the strain ductility witnessed a remarkable enhancement, whereas the peak compressive stress experienced an inconsistent trend. RMBEs built with rectangular C-shaped cross-sections exhibited comparable peak stress, smaller drop following the face shell spalling, and better strain ductility than square RMBEs. The running-bond pattern had a negative effect on both the peak stress and the strain ductility of dry RMBEs, although it exhibited comparable or even enhanced response in wet RMBEs compared to those built in the stack pattern. Pre-wetting of dry masonry shell before grouting was found to boost the peak compressive stress of unreinforced and RMBEs significantly. However, it adversely affected their strain ductility. Wet RMBEs showed a steeper post-peak descending branch compared to their dry counterparts. Indeed, the vertical reinforcement ratio and pre-wetting of dry masonry shell were the most critical parameters affecting the RMBEs peak compressive stress, whereas the confinement ratio mostly influenced the strain ductility. This study sheds light on the most critical parameters influencing the stress–strain components (i.e., strength and ductility) of RMBEs.

Strain localization and delamination mechanism of cold-drawn pearlitic steel wires during torsion

Pearlitic steel wires are cold-drawn in order to attain high strength from the alignment of the pearlite colonies along the wire axis, as well as achieve a considerable reduction in the thickness of the ferrite lamellae. However, this high level of stress, in addition to surface defects and residual stresses, drastically decreases the strain ductility in tension and often in torsion. A significant limitation in torsion is the nucleation and growth of delamination cracks which propagate along the wire. Although this fracture phenomenon has long been studied, its origin and the underlying mechanisms remain debatable. This paper presents new microstructure investigations of drawn wires during torsion. The stages of initiation and propagation are defined towards a chronology of the development phases of delamination cracks based on the study of the microstructure of cold-drawn pearlitic steel wires before and after torsion. The curling of the grains leads to the creation of long grooves on the surface of the wire. These grooves increase stress concentration during twisting, thus localizing the formation of shear bands. Deformation and strain rate are so high in these bands that nanograins (10–30 nm) are formed. The delamination then appears to be mainly due to the localization of the single-shear deformation along the wire axis with mainly intergranular crack propagation.